It is often desired to determine the ambient temperature of a fluid. A typical system includes a temperature sensor connected to a display unit. One application for such a temperature sensing system would include sport fishing.
To be successful, a fisherman needs to locate the bait or lure in an appropriate region of water to entice the fish to bite. One parameter of effective location of the bait is water temperature. Various species of fish appear to prefer different water temperatures. In an effort to locate the bait near where the desired species of fish might be situated, temperature readings are taken of the water to determine where to place the bait.
The bait is positioned with a boat mounted downrigger. The downrigger includes a frame which rotatably supports a reel which stores and dispenses the downrigger line. A downrigger arm extends from the frame and includes a guide arrangement at its free end for guiding the line from the downrigger reel into and out of the water. A trolling weight or ballast is attached to a free end of the downrigger line.
Fishing line from a fishing rod and reel is attached to an automatic release device carried by the downrigger line. A free end of the fishing line carries a hook and bait or a lure. The downrigger line and release device are lowered into the water so that the fishing line and bait or lure are lowered to the desired depth by the trolling weight.
The boat upon which the downrigger system is mounted is then moved through the water at trolling speeds. The fishing line and bait or lure will trail behind the boat at the desired depth. When a fish strikes the bait or lure, the fishing line is automatically released from the downrigger line. The fisherman then exercises his skill with the fishing rod in order to catch the fish.
Water temperature can be determined in several different ways. A temperature sensing system, separate from the downrigger, could have its own dedicated electrical line. A temperature sensor could be attached to a free end of the electrical line. This electrical line could be reeled out a certain distance. A temperature reading could then be taken. When a satisfactory temperature is found, the downrigger could then be reeled out a similar distance. The bait or lure should then be positioned in water of the desired temperature.
In an effort to improve the accuracy and to avoid duplication, previous systems have combined the temperature sensing system with the downrigger line. In such an arrangement, the sensing device, typically a thermister or a thermocouple, would be located on or near the trolling weight. The downrigger line can also function as an electrical cable and is electrically coupled to the sensing device. That cable is also coupled to an indicator in the boat. The indicator displays the temperature detected by the sensor.
One problem inherent in known systems is that they are designed to operate with a predetermined resistance between the sensor in the water and the indicator in the boat.
This resistance or impedance is due, at least in part, to the electrical cable itself. In addition impedance is due to connectors used to attach the electrical cable to the other members of the system. Typically, one or more slip rings are used to electrically connect the cable to the display. The slip ring or rings allows rotation of the cable but provide for continuous electrical contact between the cable and the indicator. The slip ring or rings can exhibit a variable impedance. Other elements of the system can also exhibit impedance.
Over time in the rugged conditions presented on a fishing boat, especially those experienced while salt water fishing, corrosion occurs and the electrical impedance of at least the slip rings may change. Although calibration can compensate for impedance changes, eventually the system becomes unreliable, and is ineffective for displaying temperature.
Thus, there exists a need for a cost-effective temperature sensing system for use in fishing which includes a temperature sensing device capable of operating substantially independently of electrical resistance in the system or changes in system resistance.